Various types of electronic systems include circuitry adapted to align transitions (or “edges”) of a first signal with transitions of a second signal. In some cases, the second signal may be a delayed version of the first signal, and edge alignment may be performed in order to align rising edges of the first signal with falling edges of the second signal, or vice versa. These types of alignment procedures may be useful, for example, to provide alignment information for other circuitry that is designed to measure signal characteristics and/or to perform signal correction, filtering or other procedures.
Some edge alignment circuits include a delay line with a plurality of series-connected delay elements. Each element in the delay line may impart a fixed-width delay, d, to the signal that it receives. Accordingly, the cumulative delay applied to a signal at the output of the nth delay element equals d×n (n=1 . . . N), where N is the number of series-connected delay elements in the delay line.
An edge-alignment circuit that includes delay elements with relatively small, fixed-width delays (a “high resolution, edge-alignment circuit”) may provide better edge alignment resolution (or accuracy) than an edge-alignment circuit that includes delay elements with relatively large, fixed-width delays (a “coarse resolution, edge-alignment circuit”). However, given a same number of delay elements, a high resolution, edge-alignment circuit may perform edge alignment for signals in a narrower frequency range than is possible using a coarse resolution, edge-alignment circuit. Accordingly, in a device in which process-voltage-temperature (PVT) ranges or other factors necessitate edge alignment over a relatively wide frequency range, a coarse resolution, edge-alignment circuit may be a preferable design choice, although at the sacrifice of more accurate edge alignment resolution. Conversely, in a device in which accurate edge alignment resolution is a more important design requirement, a high resolution, edge-alignment circuit may be a preferable design choice, although at the potential sacrifice of performance over the entire range of PVT variations.
Current edge alignment circuits are capable of providing either relatively high resolution edge alignment or edge alignment over a relatively wide frequency range, but not both. This means that circuit designers must decide whether to sacrifice either edge alignment accuracy or frequency range. However, in some cases both highly accurate edge alignment and wide operable frequency ranges are desirable. Accordingly, what are needed are edge alignment apparatus that are capable of providing relatively high resolution edge alignment for signals over a relatively wide frequency range and across a wide range of PVT variations.